Vent means for hydraulic circuit



Sept. 10, 1968 A. WIRTZ 3,400,634

VENT MEANS FOR HYDRAULIC CIRCUIT Filed Oct. 21, 1966 2 Sheets-Sheet 1 INVENTOR. EDWARD A. WIRTZ ATTORNEYS Sept. 10, 1968 E. A. WIRTZ 3,400,634

VENT MEANS FOR HYDRAULIC CIRCUIT Filed Oct. 21, 1966 v 2 Sheets-Sheet 2 r46 *48 44 EJ eafi 50 1 4 N F 556' szfilrl RESERVOIR |24 INVENTOR.

EDWARD A. WIRTZ ATTORNEYS United States Patent 3,400,634 VENT MEANS FOR HYDRAULIC CIRCUIT Edward A. Wirtz, Joliet, Ill., assignor to Caterpillar Tractor Co., Peoria, [1]., a corporation of California Filed Oct. 21, 1966, Ser. No. 588,481 2 Claims. (Cl. 91358) ABSTRACT OF THE DISCLOSURE A hydraulically actuated control device is provided for automatically arresting the operation of a fluid motor during preselected portions of an operating cycle. The control device has means for selectively venting the hydraulic circuit to a zone of reduced pressure only after operation of the motor has been arrested.

This invention relates to a hydraulic control device and more particularly to a device for venting the hydraulic circuit during each cycle of operation and for conditioning the hydraulic circuit to interrupt operation of a hydraulic motor.

This invention can be employed to control the flow of actuating pressure fluid to hydraulic motors, particularly linear actuators, in order to interrupt operation of the motor at a desired time, thus positioning an element, whether it be a linkage mechanism, a turntable, or a boom, which is actuated by the motor, at any particular location.

The invention is particularly applicable to tractormounted loaders of the kind employed for digging earth with a scoop or bucket. Although controls of this general type are known and have been relatively successful in providingautomatic positioning of a loader bucket, problems have arisen relating to the entrainment of air in the hydraulic system causing erratic operation and at times rendering the automatic positioning mechanisms inoperative until such time as the air is purged from the system. This invention provides a hydraulic circuit which includes a master-slave hydraulic cylinder assembly having a cyclically operable valve which is effective, during each cycle of operation of the positioning mechanism, to vent the hydraulic circuit to the atmosphere and thereby maintain the hydraulic circuit free of entrapped air.

Moreover, one of the principal objects of this invention is to provide a single circuit system which will vent itself of entrapped air during each cycle of operation and still provide the entire system pressure for arresting operation of a fluid motor. Thus the system prevents any loss of pressure due to venting during the motor arresting portion of the operating cycle.

Another object of this invention is to provide a hydraulically actuated positioning mechanism wherein the hydraulic circuit is cyclically vented to the atmosphere.

Another object of this invention is to provide a shiftable hydraulic motor valve to vent a portion of the working fluid to a zone of reduced pressure in order to purge and thus maintain the working fluid free of entrapped air. 7

Another object of this invention is to employ the pressure fluid of the main hydraulic circuit to operate a control device which arrests movement of a positioning mechanism at a desired point.

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawings.

In the drawings:

FIG. 1 shows a wheeled vehicle having a bucket positioning mechanism incorporating the control device of this invention;

FIG. 2 is a diagrammatic, partially in section, of the hydraulic circuit of this invention; and

FIG. 3 is an enlarged sectional view of the novel master-slave hydraulic cylinder assembly of the present invention.

Referring to FIG. 1, a loading apparatus generally indicated by the numeral 10 includes a bucket 12 pivotally connected at 14 to a pair of arms 16. The arms 16 are pivotally connected at 18 to the frame of the loading apparatus with pivotal movement of the arms 16 about the pivot connection 18 being effected by a hydraulic motor 20, preferably a jack. The bucket 12 is interconnected to a tilt motor 22 by a linkage system 24 which operates to hold or retain the bucket 12 in a fixed position relative to the horizontal as it is raised. Retraction of the motor 22 causes the link-age mechanism 24 to effect pivotal movement of the bucket 12 about the pivot 14 thus dumping the contents from the bucket.

The hydraulic circuit for operating the hydraulic motors 20 and 22 includes a lift kick-out mechanism 26 operating to interrupt flow of hydraulic fluid to the motor 20 when the arms 16 have been raised to a predetermined position and a cam kick-out mechanism 28 operating to control the action of the motor 22 in order to effect tilting of the bucket 12 about the pivot connection 14 when the arms 16 are in their raised position.

As shown in FIG. 2, the portion of the hydraulic circuit for actuating the motor 20 comprises a reservoir 30 which contains hydraulic fluid that is distributed to the circuit by a pump 32 having the discharge port thereof connected to the inlet port of a control valve 34 by a conduit 36. A conventional relief valve 38, located in a branch conduit 40, maintains the pump discharge pressure at a predetermined value by operating to return a portion of the pressure fluid to the reservoir through the conduit 40 and a conduit 42 open to the reservoir 30.

Pressure fluid from the conduit 36 is discharged to communicating passageways 44 and 46 formed in the body of the control valve 34. A check valve 48 operates in response to the level of pressure in the passageway 46 to establish communication between the passageway 46 and another passageway 50 which communicates pressure fluid to a bore 54 containing a reciprocable control spool 52. The bore 54 is formed with a plurality of longitudinally spaced annular recesses 56a, 56b, 56c, 56d, which in conjunction with the lands of the spool control the flow of pressure fluid through the valve 34. The passageway 44 distributes pressure fluid to a generally Ushaped cavity 58 and a port 60 to which is connected the conduit 42 to thereby return the pressure fluid to the reservoir 30. A conventional spring centering mechanism 62 is provided for restraining or biasing the spool 52 in a neutral position, which is the position illustrated in the drawing. While in the neutral position, it will be noted that the passageway 44 is in communication with the cavity 58 so that fluid discharged by the pump 32 is immediately returned to reservoir 30 by the conduit 42.

The spool 52 is adapted to assume various adjusted positions indicated by the letters R, N, L, and F being respectively, the raise position wherein pressure fluid is communicated to the motor 20 effecting extension thereof, a neutral position wherein fluid is returned directly to the reservoir 30, the lower position wherein fluid is communicated to the motor 20 in order to effect retraction thereof, and a float position wherein fluid is communicated to the rod end and head end of the fluid motor 20 permitting the bucket to be lowered by gravity and to be able to freely follow the terrain over which it is being moved. The annular recesses 56a and 56d have extending therebetween an internal passageway 64 defining a fluid flow path for returning fluid exhausted from the head end of the hydraulic motor 20 to the recess 56d, through the cavity 58 and to the reservoir by the conduit 42. The recess 56b communicates pressure fluid from the passageway to the head end of the motor 20 by a port 66 and a conduit 68 whereas pressure fluid communicated to the recess 560 by the passageway 50 is communicated, by a port and a conduit 72, to the rod end of the motor 20.

Assuming that it is desired to extend the fluid motor 20, the operator positions the spool 52 adjacent the position indicated by the letter R, blocking communication between the passageway 44 and the U-shaped cavity 58 and establishing communication between the passageway 50 and the discharge port 66. Under these circumstances the pressure fluid from the pump increases the pressure in the passageway 46 to a sufficient value to cause opening of the check valve 48 and allowing the pressure fluid to flow through the passageway 50 into the annular recess 56b and through the discharge port 66 and the conduit 68 to the head end of the hydraulic motor 20 thus causing extension thereof.

Retraction of the hydraulic motor 20 is accomplished by moving the spool 52 in the position indicated by the letter L establishing communication between the passageway 50 and the conduit 70 and between the conduit 68 and the passageway 64. With the check valve 48 open, pressure fluid is distributed to the hydraulic motor 20 by the conduit 72 causing retraction of the motor 20. The fluid exhausted from the head end of the hydraulic motor 20 flows through the conduit 68 to the annular recess 56b, to the annular recess 56a, through the passageway 64 and to the annular recess 56d which is in communication with the discharge port 60 thus returning the exhausted fluid to the reservoir 30 by the conduit 42.

The lift kick-out mechanism 26 includes a valve operating in response to the pivotal movement of the arm 16 for communicating pressure fluid derived from the control valve 34 to a master-slave assembly S. Operation of the slave assembly S is effective to release a detent mechanism D thereby conditioning the control valve 34 to interrupt the flow of pressure fluid to the motor 20 and thus halt pivotal movement of the arms :16.

In accordance with the basic features of this invention the hydraulic system illustrated in FIG. 2 is arranged to employ the high pressure fluid for releasing the detent mechanism D and means are incorporated in the slave assembly 5 for selectively venting the hydraulic circuit in order to purge air which may be entrained in the hydraulic system.

As shown, the spool 52 has an extension 74 pivotally connected to an actuating lever 76 mounted for rota tion with a shaft 78 which is rotatably mounted in a r bracket 80 secured to the frame of the machine. Shifting of the spool to any of the indicated positions is accomplished when the operator rotates the shaft 78 in turn rotating the lever 76 thus effecting reciprocation of the spool 52. In addition to the lever 76 the detent mechanism D comprises another lever 82 pivotally connected to the frame of the machine at 84 and formed with a laterally projecting support arm 86 on the end of which is rotatably mounted a roller 88. The lever 82 is urged in a clockwise direction by a spring 90 having one end attached to the lower end of the lever 82 and the remaining end attached to a small bracket 92 secured to the body of the slave assembly S.

The lower end of the actuating lever 76 is formed with cam surfaces 94, 96 and 98 against which the roller 74 is held in engagement by the spring 90. These cam surfaces are effective in conjunction with the force of the spring 90 to retain the lever 76 and the spool 52 in a desired adjusted position.

-It can be seen that rotation of the lever 76 in order to position the spool 52 of the valve 34 in the raised position rotates the lower end of the lever 76 in a counterclockwise direction permitting the roller 88 to come in rolling contact with the cam surface 94 and thus cause, by virtue of the spring 90, clockwise rotation of the lever 82. When the roller 88 is in contact with the cam surface 94, the spool 52 is held in the raised position.

Another important feature of this invention pertains to a high pressure kick-out mechanism operating to communicate pressure fluid discharged through the conduit 68 to the slave assembly S in order to rotate the lever 82 of the detent mechanism in a counterclockwise direction thereby returning the spool 52 to its neutral position and interrupting movement of the arms 16 at a desired raised position.

As shown in FIG. 2, the kick-out mechanism comprises a base plate 100 rigidly mounted on the arms 16 by plurality of bolts 102. A bracket 104, secured to the plate 100 has a cam 106 secured thereon in any suitable manner and preferably as shown by means of a bolt 108. A valve 110 is rigidly supported on a boss 111, forming part of the frame of the loading apparatus. This valve includes a spool 112 having an outward extension 114 on the end of which is rotatably mounted a roller 116. The spool 112 is normally held in the illustrated position by a spring 118 located within the bore of the valve.

Passageway 119 is provided for communicating with a drain during certain sequences of operation. The valve 110 is connected by means of a conduit 120 to the conduit 68 and by means of a conduit 122 to the slave assembly S. During such times that the control valve 34 is adjusted to discharge pressure fluid from the pump 32 t0 the conduit 68 in order to pressurize the head end of the motor 20, the cam 106 engages the roller 116 moving the spool 112 to the right (as viewed in FIG. 2) thereby establishing communication between the conduit 120 and 122 thus communicating pressure fluid to the slave assembly S.

When the spool 52 is shifted leftwardly in order to admit pressure fluid to the conduit 68 causing extension of the motor 20, the actuating lever 76 is rotated in a counterclockwise direction and the lever 82 by virtue of the spring 90 is rotated in a clockwise direction establishing rolling engagement between the roller 88 and the cam surface 94.

The slave assembly S is hydraulically arranged with the valve 110 and mechanically arranged with the detent mechanism D to vent the fluid in the conduit 122 and to permit the spring centering mechanism 62 to return the spool 52 to its neutral position when the arms 16 have reached a predetermined raised position.

As shown in FIG. 3, the master-slave assembly S comprises a main housing 124 having a valve spool 126 reciprocably mounted therein. Valve spool 126 has a first annular groove 128 formed between a first land portion 130 and an intermediate land portion 132. Similarly, a second annular groove 134 is formed on the spool 126 between the intermediate land 132 and a third land portion 136. An elongated rod portion 138 extends outwardly from one end of the spool 126 and is pivotally connected at 140 to the lower portion of lever 82.

A passageway 142 (shown in dotted outline) in the spool 126 establishes fluid communication between annular groove 134 and spool cavity 144. Cavity 144 communicates with reservoir 30 via a first small diameter bleed conduit 146 and a second small diameter bleed conduit 148. Conduits 146 and 148 are preferably conveniently joined to a conduit 150 for leading to the reservoir 30.

A small ball check valve 152 is positioned in conduit 148 for selectively preventing fluid in cavity 144 from draining to reservoir 30. A floating piston 154 is positioned in a passageway 156 which is always open to the pressure in conduit 122 via one of the annular spool recesses 128 or 134. Passageway 156 and floating piston 154 are of substantially greater diameter than the bleed conduit 148. Consequently, equal pressures in cavity 144 and passageway 156 would result in ball check 152 blocking conduit 148 from draining to reservoir 30. A spacer plug 158 is provided to limit the lateral movement of the floating piston 154.

In describing the operation it will be assumed that the hydraulic motor is to be extended thereby raising the arms 16. The operator eflects rotation of shaft 78 thereby causing lever 76 to move to position R and the detent mechanism D is adjusted so that roller 88 is in contact with the cam surface 94. Since the biasing force of spring 90 exceeds the pressure in the slave assembly cavity 144, the spool 126 will move leftwardly into the cavity.

At this time the ball check 152 moves to the right and allows the fluid in cavity 144 to vent to reservoir 30 via conduit 148. As the arms 16 reach their predetermined raised position, the spool 112 of the valve is shifted by the cam 106 to establish communication between the conduits and 122 thereby communicating pressure fluid to the slave assembly S. Valve spool 126 is at this time positioned sufliciently far to the left to provide communication between the conduit 122 and the passageway 156 via the annular groove 134. At this juncture it should be noted that the ball check 152 instantly seats to block off the drain conduit 148 due to floating piston 154 having a greater cross-sectional area than the passage way 148. Thus, at this critical phase of the operation the entire pressure fluid of the circuit is passed through spool passageway 142 to the cavity 144 which causes instant rightward movement of the spool 126 since the pressure in chamber 144 is greater than the biasing force of spring 90. Such shifting of spool 126 in turn causes counterclockwise rotation of the lever 82 and consequent disengagement of roller 88 from the cam surface 94. Thus, the spring centering mechanism 62 of the control valve 34 is made effective to position the spool 52 in a neutral position blocking flow of pressure fluid to the conduit 68 to arrest further extension of motor 20. After the spool 126 has moved to the right to approximately the position shown in FIG. 3, any air that may be entrapped in the hydraulic system is purged through reduced diameter conduit 146 back to reservoir 30. Once the conduit 68 has been blocked by the valve spool 52, the spring 118 causes the valve spool 112 to move to the position shown in FIG. 2 thereby opening conduit 122 to drain via passageway 119. Also, it will be apparent that after valve spool 126 of the slave assembly moves to the position shown in FIG. 3 the ball check 152 will unseat and thereby open bleed conduit 148 to reservoir 30.

Thus, the novel master-slave assembly S is effective during one portion of the operating cycle (raising of arms 16) to direct the entire volume of fluid under pressure in conduit 122 to cause a quick release of the detent mechanism D thereby preventing faulty operation through loss of fluid pressure during this critical period. On the other hand, the master-slave assembly S is also effective. during another portion of each operating cycle, to purge any air that may be entrapped in the hydraulic system.

Although the subject hydraulic system has been disclosed and described in relation to a loader bucket lift system, it could also be applied to the bucket tilt controls for automatically interrupting movement of the bucket at its proper loading position when rotating between a dump and tilt-back position. It is also conceivable that the system could be applied to the control of any implement where it is desirable that the implement being actuated be automatically stopped in a predetermined position.

What is claimed is:

1. A control device for a hydraulic circuit comprising a movable support, a hydraulic motor being arranged to impart movement to said support, a control valve mechanism for communicating pressure fluid to said motor to cause operation thereof, means including a pressure operated device connected to the circuit for maintaining said valve mechanism in a position communicating pressure fluid to said motor, and means actuated in response to the position of said support and being operable to communicate pressure fluid to said pressure operated device for disconnecting said motor from a source of pressure fluid in order to arrest movement of said movable support, said pressure operated device further having means for selectively venting said circuit to a zone of reduced pressure after said motor has been disconnected from said source of pressure fluid.

2. A control device as set forth in claim 1 wherein said hydraulic motor comprises a double acting linear actuator, said control valve having a spool reciprocably mounted therein and adjustable to communicate pressure fluid to said actuator to effect extension and retraction thereof, a detent mechanism rendered operative when said spool is adjusted to effect extension of said actuator and maintain said spool in its adjusted position, said pressure operated device comprising a fluid operated detent release mechanism including a housing having a reciprocable valve element formed with land portions and a rod portion, means effective upon extension of said actuator for communicating pressure fluid from said control valve to an annular recess formed between land portions intermediate said reciprocal valve element, a passageway in said valve element communicating fluid from said annular recess to a chamber defined by one of said lands and said housing to effect shifting of said valve element, said valve element being connected to said detent mechanism so that upon shifting thereof said detent is released and said actuator disconnected from said source of pressure fluid, and vent conduit means for communicating with said chamber after said valve element has shifted to release said detent, said vent means eflective for exhausting a part of the fluid communicated to said chamber to a zone of reduced pressure to thereby purge entrapped air from the circuit.

References Cited UNITED STATES PATENTS 2,159,879 5/1939 Dewandre 9l358 2,649,076 8/1953 Dupre 9l358 3,289,546 12/1966 Erickson 9l358 FOREIGN PATENTS 549,134 11/1942 Great Britain.

PAUL E. MASLOUSKY, Primary Examiner. 

